Parasite susceptibility in an amphibian host is modified by salinization and predators

Secondary salinization represents a global threat to freshwater ecosystems. Salts, such as NaCl, can be toxic to freshwater organisms and may also modify the outcome of species interactions (e.g. host-parasite interactions). In nature, hosts and their parasites are embedded in complex communities where they face anthropogenic and biotic (i.e. predators) stressors that influence host-parasite interactions. As human populations grow, considering how anthropogenic and natural stressors interact to shape host-parasite interactions will become increasingly important. We conducted two experiments investigating: (1) the effects of NaCl on tadpole susceptibility to trematodes and (2) whether density- and trait-mediated effects of a parasite-predator (i.e. damselfly) and a host-predator (i.e. dragonfly), respectively, modify the effects of NaCl on susceptibility to trematode infection. In the first experiment, we exposed tadpoles to three concentrations of NaCl and measured parasite infection in tadpoles. In the second experiment, we conducted a 2 (tadpoles exposed to 0 g L^-1 NaCl vs. 1 g L^-1 NaCl) x 4 (no predator, free-ranging parasite-predator (damselfly), non-lethal host-predator (dragonfly kairomone), and free-ranging parasite-predator + dragonfly kairomone) factorial experiment. In the absence of predators, exposure to NaCl increased parasite infection. Of the predator treatments, NaCl only caused an increase in parasite infection in the presence of the parasite-predator. However, direct consumption of trematodes caused a reduction in overall infection in the parasite-predator treatment. In the dragonfly kairomone treatment, a reduction in tadpole movement (i.e. trematode avoidance behavior) led to an increase in overall infection. In the parasite-predator + dragonfly kairomone treatment, antagonistic effects of the parasite-predator (reduction in trematode abundance) and dragonfly kairomone (reduction in parasite avoidance behavior) resulted in intermediate parasite infection. Collectively, these findings demonstrate that NaCl can increase amphibian susceptibility to parasites, and underscores the importance of considering predator-mediated interactions in understanding how contaminants influence host-parasite interactions.

Intra- and intersexual differences in parasite resistance and female fitness tolerance in a polymorphic insect

To understand host-parasite interactions, it is necessary to quantify variation and covariation in defence traits. We quantified parasite resistance and fitness tolerance of a polymorphic damselfly (Ischnura elegans), an insect with three discrete female colour morphs but with monomorphic males. We quantified sex and morph differences in parasite resistance (prevalence and intensity of water mite infections) and morph-specific fitness tolerance in the females in natural populations for over a decade. There was no evidence for higher parasite susceptibility in males as a cost of sexual selection, whereas differences in defence mechanisms between female morphs are consistent with correlational selection operating on combinations of parasite resistance and tolerance. We suggest that tolerance differences between female morphs interact with frequency-dependent sexual conflict, which maintains the polymorphism locally. Host-parasite interactions can therefore shape intra- and intersexual phenotypic divergence and interfere with sexual selection and sexual conflict.

Resistance to Arrenurus spp. Parasitism in Odonates: Patterns Across Species and Comparisons Between a Resistant and Susceptible Host

Some adult odonates resist parasitism by larval water mites (Arrenurus spp.) with melanotic encapsulation, in which the mite's stylestome is clogged and the mite starves. In summer 2014, we counted the engorged and resisted mites on 2,729 adult odonates sampled by aerial net at 11 water bodies in Greenville Co. and Pickens Co., SC, and tested the hypothesis that the frequency and intensity of resistance correlates with parasite prevalence (the percentage of parasitized hosts). Resistance prevalence (the percentage of parasitized hosts that resisted at least one mite) varied significantly among host species, exceeding 60% for Argia fumipennis(Burmeister) and Celithemis fasciata Kirby but less than 20% for other species. However, neither resistance prevalence nor mean resistance intensity (mean percentage of resisted mites on resisting hosts) correlated with parasite prevalence. We described potential effects of parasitism on host development ofA. fumipennis and Pachydiplax longipennis(Burmeister) by comparing the percent asymmetry of forewing lengths between parasitized and unparasitized individuals. There was no significant difference in asymmetry for either males or females of A. fumipennis, or males of Pa. longipennis(females were not sampled). We also evaluated differences in melanotic encapsulation between A. fumipennis, which readily encapsulates mites in nature, and Pa. longipennis We inserted a 2.0-mm piece of sterile monofilament line into the thorax of captured individuals for 24 h and compared mean gray value scores of inserted and emergent ends using Image-J software. There was no difference in melanotic encapsulation between species.

MORPHOLOGY AND ULTRASTRUCTURE OF TWO SCHISTOTAENIID CYSTICERCOIDS (CESTODA: CYCLOPHYLLIDEA) FROM THE HAEMOCOELE OF THE DRAGONFLY LARVAE

Two cysticercoids, belonging to ascocercus type, namely euascocercus and multicercus, were found in haemocoele of dragonfly larvae of the genus Aeshna from the lakes of the Magadan Province. The cysticercoid of Schistotaenia srivastavai Raush, 1970 (euascocercus) is formed of the outer (exocyst) and inner (endocyst) envelopes, containing the scolex and larval strobila. The outer and inner surfaces of the exocyst are represented by the tegument covered with microvilli. The microvilli of the outer tegument are restricted by the surface layer, consisting of granular and fibrillar material, and possess different structures at different stages of post-embryonic development. The multicercus of Mircia shigini (Konyaev et Gulyaev, 2006) is able to multiply asexually by the endogenous budding. The daughters' individuals are formed in the envelope of the multicercus that represents the tegument bearing microvilli. These microvilli are also restricted by the surface layer. The morphology and development of each individual cysticercoid of the multicercus is similar to those of euascocercus. The production of a great amount of cysticercoids, and the presence of the surface layer resembling the laminated layer of Echinococcus, relates multicercus to hydatid cysts.

Ultrastructural study of protective envelopes in Dioecocestus asper (Cestoda: Dioecocestidae) megalocercus

The megalocercus of Dioecocestus asper (Mehlis 1831) from the haemocoele of dragonfly larvae possesses two envelopes: outer (exocyst) and inner (endocyst) ones. The exocyst contains the large endocyst and larval strobila with scolex attached to the latter. Outer and inner surfaces of these envelopes are organized as the tegument and have some structural differences. The exocyst is covered with slender microvilli. Its outer tegument contains numerous mitochondria; the inner one is filled with lipid droplets released into the exocyst's cavity. The well-developed protonephridial (excretory) system consisting of flame cells, collecting ducts and canals is the unique feature of the exocyst, noted for the first time. Thick (more, then 50 microm) distal cytoplasm of the outer tegument of the endocyst is the place of accumulation of uniform globules looking like a hyaloid layer. This outer layer together with underlying fibrous layer (up to 20 microm), apparently, protect the scolex and larval strobila during the transfer through feather clump in the stomach of grebes, definitive hosts of D. asper. Muscle cells of both envelopes retain their synthetic activity even in the fully developed metacestode. Probably, they are the main structural element, which produces fibers of the extracellular matrix and maintains the integrity of protective envelopes of the megalocercus.

Hydrophylita (Lutzimicron) emporos Shih & Polaszek (Hymenoptera: Trichogrammatidae) from Taiwan, parasitising eggs, and phoretic on adults, of the damselfly Psolodesmus mandarinus mandarinus (Zygoptera: Calopterygidae)

Hydrophylita emporos n. sp. reared from eggs of Psolodesmus mandarinus mandarinus McLachlan (Zygoptera: Calopterygidae) in Taiwan is described. This is the first species of Hydrophylita to be described from the Old World, and the first record of phoresy in the genus. Adult females were observed aggregating at the base of the female damselfly’s abdomen. When the damselfly begins ovipositing, females move to the tip of the abdomen, enter the water and quickly locate eggs for parasitising. The article contains links to video footage of this process.

[On the life cycle and morphology of metacestodes Dioecocestus asper (Cyclophyllidea: Dioecocestidae)]

Metacestodes Dioecocestus asper (Cyclophyllidea) habe been found in larvae of dragonflies Aeshna spp. (Odonata, Anisoptera) from the lakes of the Upper Kolyma and northern Okhotsk seaboard basins (3.8 +/- 0.46 % of n = 1730 and 0.09 +/- 0.09 % of n = 1065, respectively) for the first time. Thus, participation of dragonflies in lifecycle of Dioecocestidae has been proved. Larvagenesis of D. asper (from spontaneously infested hosts) have been retraced from the stage of primary lacuna up to fully-developed metacestode. Process of development of the metacestode D. asper includes two invaginations. The first one follows the start of exogenous formation of undifferentiated anlage of the cystoscolex; as the result, the latter settles to the bottom of the forming two-layered exocyst homologous to the cercomer. Subsequent development of the prospecive part and the endocyst occurs in the closed amniotic cavity of the sacciform exocyst, the back pole of which preserves embryonic hooks and the front pole possesses the invaginational channel. At the stage of early scolexogenesis, the endocyst with the anlage of the strobila and the scolex separates from the exocyst and the excretory atrium forms on the back pole of endocyst. At the stage of late scolexogenesis, the formation of the larval strobila (differentiation of the sex) is completed and the second invagination starts. Strong retractors pull bottom of the stribila into the endocyst; simultaneously, the front part of it is also turned inside. The invaginational pore of the endocyst of fully-developed metacestode D. asper remains open; the scolex with the most part of the strobila is located outside the endocyst in the cavity of the exocyst. The encystment of the metacestode occurs when the temperature rises up to 40 degrees C (i. e., reaching the temperature of the definitive host). Morphogenesis of the uniquely large (among the cyclophyllid metacestodes developing in the invertebrate intermediate host) metacestode D. asper lasts for about two--three years and is associated with the developmental terms of the intermediate host, the larva of the Aeshna dragonfly, in climatic conditions of the Far North-East of Asia. Early stages of morphogenesis of D. asper were noted at the dragonfly larvae of the age of 0+ (at September) and 1+ (at June), and fully-developed metacestodes, only at elder ages. Owing to the extremely large size of D. asper metacestodes we refer them as a specific modification of cysticercoids: a megalocercus (Megalocercus). Common features were noted in the structure and morphogenesis of D. asper megalocercus and ascocerci of Schistotaeniidae. High morphological similarity of these metacestodes and their development in relative taxonomic groups of intermediate hosts, larvae of amphibiotic insects (the dragonfly larvae, and occasionally the larvae of mayflies or water-bugs), prove their belonging to the same philogenetically related group of metacestodes Cyclophyllidea, emerging independently from other groups of cysticercoids. We suggest naming this morpho-ecological group of larvocysts as ascocerci (or ascocysticercoids). The use of the name "ascocercus" as nominal nomenclature for group of larvocysts supposes the change of the name "ascocercus Schistotaeniidae" to "euascocercus".